Plans sometimes have exclusions for coverage related to "illegal acts" that could leave people on the hook for at least part of their medical costs. But health policy experts said it's unclear how common these clauses are or when they're used.

Hospitals around the country are afraid to send out hundreds of thousands of bills related to COVID-19 testing. That's because Congress mandated there would be no copays and no out-of-pocket costs for patients. But who's paying?